02Label color crossfade

<main class="stage">
  <div class="fv2 is-demo">
    <span class="fv2__label-wrap">
      <span class="fv2__label fv2__label--neutral">Nickname</span>
      <span class="fv2__label fv2__label--ok">This nickname is available</span>
    </span>
    <input class="fv2__input" type="text" value="godrich_dev" readonly>
  </div>
</main>

@use "../../../../site/static/demo-tokens" as *;

// 닉네임 라벨 두 장을 겹쳐두고, 검증 상태에 따라 opacity 만 서로 교차한다
$duration: $dur-loop;
$easing: $ease-out;
$color: $subject-mint;

@include stage($stage-yellow);

.fv2 { width: min(240px, 86vw); display: flex; flex-direction: column; gap: $sp-2; }
.fv2__label-wrap { position: relative; height: 14px; display: block; }
.fv2__label {
  position: absolute; left: 0; top: 0; font-weight: 600; font-size: 12px; line-height: 1; font-family: inherit;
  white-space: nowrap;
}
.fv2__label--neutral { color: $subject-ink; opacity: .6; }
.fv2__label--ok { color: $color; opacity: 0; }
.fv2__input {
  box-sizing: border-box; width: 100%; padding: $sp-2 $sp-3; border-radius: $r-sm;
  border: 2px solid $subject-ink; background: rgba(23, 20, 26, .06);
  color: $subject-ink; font-weight: 400; font-size: 14px; line-height: 1; font-family: inherit;
}

@keyframes fv2-ok {
  0%, 20% { opacity: 0; }
  40%, 90% { opacity: 1; }
  100% { opacity: 0; }
}
@keyframes fv2-neutral {
  0%, 20% { opacity: .6; }
  40%, 90% { opacity: 0; }
  100% { opacity: .6; }
}
.fv2.is-demo .fv2__label--ok { animation: fv2-ok $duration $easing infinite; }
.fv2.is-demo .fv2__label--neutral { animation: fv2-neutral $duration $easing infinite; }

// 한 겹(감쇠 진동): ok 라벨 등장(40%) 순간 필드에 미세 translateX 감쇠 shake + 민트 글로우가 box-shadow spread 로 한 번 번지는 surge 파동
// (input 요소엔 ::after 가 렌더되지 않으므로 링은 box-shadow spread 로 구현)
.fv2.is-demo .fv2__input {
  animation: fv2-shake $duration $easing infinite, fv2-surge $duration $easing infinite;
}

@keyframes fv2-shake {
  0%, 40%, 46%, 100% { transform: translateX(0); }
  41.5% { transform: translateX(.8px); }
  43% { transform: translateX(-.5px); }
  44.5% { transform: translateX(.25px); }
}
@keyframes fv2-surge {
  0%, 40% { box-shadow: 0 0 0 0 rgba($subject-mint, 0); }
  42% { box-shadow: 0 0 0 6px rgba($subject-mint, .5); }
  44% { box-shadow: 0 0 0 2px rgba($subject-mint, .22); }
  46% { box-shadow: 0 0 0 3.5px rgba($subject-mint, .3); }
  50%, 100% { box-shadow: 0 0 0 0 rgba($subject-mint, 0); }
}

@media (prefers-reduced-motion: reduce) {
  .fv2.is-demo .fv2__label--ok,
  .fv2.is-demo .fv2__label--neutral { animation: none !important; }
  .fv2.is-demo .fv2__label--ok { opacity: 1; }
  .fv2.is-demo .fv2__label--neutral { opacity: 0; }
  .fv2.is-demo .fv2__input { animation: none !important; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.fv2 {
  width: min(240px, 86vw);
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.fv2__label-wrap {
  position: relative;
  height: 14px;
  display: block;
}

.fv2__label {
  position: absolute;
  left: 0;
  top: 0;
  font-weight: 600;
  font-size: 12px;
  line-height: 1;
  font-family: inherit;
  white-space: nowrap;
}

.fv2__label--neutral {
  color: #17141a;
  opacity: 0.6;
}

.fv2__label--ok {
  color: #4cd4a6;
  opacity: 0;
}

.fv2__input {
  box-sizing: border-box;
  width: 100%;
  padding: 8px 12px;
  border-radius: 8px;
  border: 2px solid #17141a;
  background: rgba(23, 20, 26, 0.06);
  color: #17141a;
  font-weight: 400;
  font-size: 14px;
  line-height: 1;
  font-family: inherit;
}

@keyframes fv2-ok {
  0%, 20% {
    opacity: 0;
  }
  40%, 90% {
    opacity: 1;
  }
  100% {
    opacity: 0;
  }
}
@keyframes fv2-neutral {
  0%, 20% {
    opacity: 0.6;
  }
  40%, 90% {
    opacity: 0;
  }
  100% {
    opacity: 0.6;
  }
}
.fv2.is-demo .fv2__label--ok {
  animation: fv2-ok 2s ease-out infinite;
}

.fv2.is-demo .fv2__label--neutral {
  animation: fv2-neutral 2s ease-out infinite;
}

.fv2.is-demo .fv2__input {
  animation: fv2-shake 2s ease-out infinite, fv2-surge 2s ease-out infinite;
}

@keyframes fv2-shake {
  0%, 40%, 46%, 100% {
    transform: translateX(0);
  }
  41.5% {
    transform: translateX(0.8px);
  }
  43% {
    transform: translateX(-0.5px);
  }
  44.5% {
    transform: translateX(0.25px);
  }
}
@keyframes fv2-surge {
  0%, 40% {
    box-shadow: 0 0 0 0 rgba(76, 212, 166, 0);
  }
  42% {
    box-shadow: 0 0 0 6px rgba(76, 212, 166, 0.5);
  }
  44% {
    box-shadow: 0 0 0 2px rgba(76, 212, 166, 0.22);
  }
  46% {
    box-shadow: 0 0 0 3.5px rgba(76, 212, 166, 0.3);
  }
  50%, 100% {
    box-shadow: 0 0 0 0 rgba(76, 212, 166, 0);
  }
}
@media (prefers-reduced-motion: reduce) {
  .fv2.is-demo .fv2__label--ok,
  .fv2.is-demo .fv2__label--neutral {
    animation: none !important;
  }
  .fv2.is-demo .fv2__label--ok {
    opacity: 1;
  }
  .fv2.is-demo .fv2__label--neutral {
    opacity: 0;
  }
  .fv2.is-demo .fv2__input {
    animation: none !important;
  }
}

import type { CSSProperties } from "react";
import styles from "./LabelColorShift.module.scss";

export type LabelColorShiftProps = { duration?: number; easing?: string; color?: string };
type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };

export default function LabelColorShift({ duration = 2000, easing = "ease-out", color = "#4cd4a6" }: LabelColorShiftProps) {
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };
  return (
    <div className={styles.fv2} style={vars}>
      <span className={styles.wrap}>
        <span className={`${styles.label} ${styles.neutral}`}>닉네임</span>
        <span className={`${styles.label} ${styles.ok}`}>사용할 수 있는 닉네임이에요</span>
      </span>
      <input className={styles.input} type="text" defaultValue="godrich_dev" readOnly />
    </div>
  );
}